1. Field of the Invention
This invention relates to tripodal support structures and more particularly to a three-legged folding step-ladder having outrigger-type support extensions on the two front support legs, a rear support member having a single ground contact point, and independently extendable and retractable safety hand rails. The support legs of the instant invention contact the ground at points spaced apart from one another to form an equilateral triangle when viewed from above.
2. Description of the Prior Art
Four-point support configurations, as are universally found with stepladders, are inherently unstable against lateral tilting, due to the relatively large ratio of ladder height to width. As a user climbs higher, this instability increases due to the increase in the moment arm as measured between the ladder/ground support points and the user's body. The inherent statical indeterminacy of this configuration often results in serious injuries to users, and the risk of accident increases with the height of climb.
It is widely known that a three-point support configuration is more stable against a lateral force input than a four-point configuration, and that an equilateral support configuration provides optimal stability. For example, a surveyor's instrument, which requires near absolute rigidity for accurate performance, depends on a tripod for support. Numerous attempts have been made to provide additional lateral support to step or other ladders, but none have incorporated an equilateral tripodal support design, together with retractable safety handrails connected to the side rails of the ladder. The concepts embodied in the following list of U.S. Pats. Nos. are representative of past efforts: 479,051, 1,333,344, 4,011,926, 952,836, 1,342,881, 4,147,231, 1,134,437, 3,856,112, 4,293,055, 1,217,713, 3,891,054, 4,519,477.